1, Field of the Invention
The invention relates to a method of manufacturing a flash memory cell, and more particularly, to a method of manufacturing 2-bits flash memory cell.
2, Description of the Prior Art
Nonvolatile memories are utilized in many electronics devices for storing configuration data or program data, etc. By having advantages of repeatable write, read, and erase operations and retaining their data values even after power is removed from the device, flash memory becomes one of the widely adopted non-volatile memories in electronics devices such as personal computers, personal digital assistants, digital cameras, and digital music players.
A conventional flash memory cell includes a stacked gate upwardly including a tunnel oxide layer, a floating gate for storing electric charges, a control gate for controlling the charging of the floating gate, and an oxide-nitride-oxide (ONO) multilayer positioned between the floating gate and the control gate. By applying a bias to the control gate and the source/drain, the electrons are transferred into or from the floating gate as performing the write or erase operations. And by using a threshold voltage fluctuation depending on whether there are charges in the floating gate, the flash memory cell may store data.
With a trend toward scaling down the size of the semiconductor device to deep sub-micron feature sizes, the memory cells are accordingly required to have high integration density. Meanwhile, since throughput and storage capacity of the electronic information products keep increasing, the memory cells are required to have not only higher integration density but also larger memory capacity and higher reliability. Therefore, a method to manufacture a flash memory cell with consideration to the abovementioned issues is still in need.